virtual memory, virtual storage(noun)

(computer science) memory created by using the hard disk to simulate additional random-access memory; the addressable storage space available to the user of a computer system in which virtual addresses are mapped into real addresses

virtual memory(Noun)

Memory that appears to be RAM but is being simulated (by a process called paging) on a hard disk; allows a computer to operate as if it had more memory than it actually does, but with some loss of performance